From mboxrd@z Thu Jan 1 00:00:00 1970 From: Anatolij Gustschin Subject: Re: [PATCH v2 1/3] usb: misc: add driver for FT232H based FPGA configuration devices Date: Tue, 20 Nov 2018 15:49:47 +0100 Message-ID: <20181120154947.4dbc90d6@crub> References: <20181120002821.12794-1-agust@denx.de> <20181120002821.12794-2-agust@denx.de> <1542675372.30311.573.camel@impinj.com> Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Cc: "linux-spi@vger.kernel.org" , "linux-kernel@vger.kernel.org" , "linux-fpga@vger.kernel.org" , "linux-usb@vger.kernel.org" , "gregkh@linuxfoundation.org" , "broonie@kernel.org" , "atull@kernel.org" , "mdf@kernel.org" To: Trent Piepho Return-path: In-Reply-To: <1542675372.30311.573.camel@impinj.com> Sender: linux-kernel-owner@vger.kernel.org List-Id: linux-spi.vger.kernel.org On Tue, 20 Nov 2018 00:56:13 +0000 Trent Piepho tpiepho@impinj.com wrote: >On Tue, 2018-11-20 at 01:28 +0100, Anatolij Gustschin wrote: >> Add USB interface driver for ARRI FPGA configuration devices based on >> FTDI FT232H chip. Depending on USB PID the driver registers different >> platform devices describing an FPGA configuration interface. > >Is ARRI different than Arria? yes, ARRI is a company name. >> +/* Use baudrate calculation borrowed from libftdi */ >> +static int ftdi_to_clkbits(int baudrate, unsigned int clk, int clk_div, > >Linux uses unsigned values for clocks. Does it make any sense to mix >the unsigned clk with signed values? Seems like baudrate and clk_div >should also be unsigned. okay, will fix to unsigned. >> + unsigned long *encoded_divisor) > >unsigned long is an odd choice here. Is there any to reason to use an >unsigned long to store the result of right shifting a signed int >(best_div)? It can't be longer than a int, but it can be negative. okay, I'll change that to unsigned int. >> +{ >> + static const char frac_code[8] = { 0, 3, 2, 4, 1, 5, 6, 7 }; >> + int best_baud = 0; >> + int div, best_div; >> + >> + if (baudrate >= clk / clk_div) { >> + *encoded_divisor = 0; >> + best_baud = clk / clk_div; >> + } else if (baudrate >= clk / (clk_div + clk_div / 2)) { >> + *encoded_divisor = 1; >> + best_baud = clk / (clk_div + clk_div / 2); >> + } else if (baudrate >= clk / (2 * clk_div)) { >> + *encoded_divisor = 2; >> + best_baud = clk / (2 * clk_div); >> + } else { >> + /* >> + * Divide by 16 to have 3 fractional bits and >> + * one bit for rounding >> + */ >> + div = clk * 16 / clk_div / baudrate; >> >> + if (div & 1) /* Decide if to round up or down */ >> + best_div = div / 2 + 1; >> + else >> + best_div = div / 2; > >In Linux we would write: > >best_div = DIV_ROUND_UP(div, 2); > >Though I think you can combine that with the above to get: > >best_div = DIV_ROUND_CLOSEST(clk * 8 / clk_div, baudrate); > >That what the above is trying to accomplish in a round about way will rework this, too. Thanks for suggestions. >> + if (best_div > 0x20000) >> + best_div = 0x1ffff; >Looks like the above was probably supposed to be >= I'll check it. >> + best_baud = clk * 16 / clk_div / best_div; >> + if (best_baud & 1) /* Decide if to round up or down */ >> + best_baud = best_baud / 2 + 1; >> + else >> + best_baud = best_baud / 2; > >Again, looks like a complicated way to round to the nearest. will change this, too. Thanks, Anatolij